1. Field of the Invention
This invention relates to a connecting device between an air intake and a power plant of an aircraft nacelle.
2. Description of the Related Art
An aircraft propulsion system comprises a nacelle in which a power plant that is connected by means of a mast to the rest of the aircraft is arranged in an essentially concentric manner.
As illustrated in FIG. 1 the nacelle comprises, at the front, an air intake 10 that makes it possible to channel a stream of air into a power plant 12, a first portion of the incoming stream of air, called a primary stream, passing through the power plant to participate in the combustion, the second portion of the stream of air, called a secondary stream, being entrained by a fan and flowing into an annular pipe that is delimited by the inside wall of the nacelle and the outside wall of the power plant.
The air intake 10 comprises a lip 14 whose surface in contact with the aerodynamic streams is extended inside the nacelle via an inside pipe 16 with essentially circular cross-sections and outside of the nacelle by an outside wall 18 with essentially circular cross-sections.
Techniques have been developed for reducing the noise emitted by an aircraft, and in particular the noise that is emitted by the propulsion systems. They consist in placing—in particular at the wall of the inside pipe 16—a coating 20 whose purpose is to absorb a portion of the sound energy, in particular by using the principle of Helmholtz resonators.
In a known manner, a coating for the acoustic treatment 20, also called an acoustic attenuation panel, comprises—from the outside to the inside—an acoustically resistive porous layer 22 at least one alveolar structure 24 and a reflective or impermeable layer 26.
The acoustically resistive layer is a porous structure that has a dissipative role, partially transforming into heat the acoustic energy of the sound wave that passes through it. It comprises so-called open zones that are able to allow the acoustic waves to pass and other so-called closed or solid zones that do not allow the sound waves to pass but are designed to ensure the mechanical strength of said layer. This acoustically resistive layer is characterized in particular by an open surface area ratio that varies essentially as a function of the engine, components constituting said layer.
The air intake 10 is connected to the power plant 12 by a connection that is illustrated in detail in FIGS. 2 and 3. This connection comprises—at the power plant—an annular collar 28 with which a flange 30 is made integral. This flange has an L-shaped cross-section, of which one wing 32 is flattened against the collar 28 and is made integral with the latter by any suitable means, for example bolts or rivets 34, passing through the collar and the wing 32 of the flange and extending parallel to the longitudinal axis of the nacelle. Preferably, this flange 30 extends over the circumference of the pipe 16 and can be made of several sections. The flange 30 is connected to the air intake 10 and more particularly to the rear surface 36 of the so-called acoustic panel that delimits the inside pipe 16. For this purpose, the second wing 38 of the flange 30 is flattened against the rear surface 36 of the acoustic panel and is made integral with the latter by any suitable means, in particular bolts or rivets 40 that are oriented radially. These blind-type connecting means 40 are deemed less reliable than the conventional attachments. Consequently, the number of connecting means 40 should be significant so that they are distributed in two rows, and it is necessary to provide a structural reinforcement part 42 to ensure the connection between the flange 30 and the acoustic panel that delimits the pipe 16 of the air intake.
The presence of this structural reinforcement part 42 and the arrangement in two rows of the connecting means lead to reducing the treated surface area on the acoustic plane and to not optimizing the acoustic treatment.